Automatic control system



22, A. R. MABEY .AUTOMATIC CONTROL SYSTEM Filed Sept. 3, 1957 Paeumatz'c Reyula tor INVENTOR. ARTHUR R. MA8EY BY I 72 ATTORNEY.

Patented Aug. 22, 1939 2,17 0,418

UNITED' STATES PATENT OFFICE AUTOMATIC CONTROL SYSTEM Arthur R. Mabey,Waterbury, Conn, assignor to The Bristol Company, Waterbury, Conn., acorporation of Connecticut Application September'3, 1937, SerialNo.162,277

'6 Claims. (Cl. 236-86) This invention relates to automatic controldesirable condition would remain effective until the vices and systemsand more especially to control secondary element had attained a state ofsystems of that class wherein regulation of a equilibrium and hadreadjusted the action of its variable condition in response to physicalchanges opposed elements in keeping with conditions reptherein iseffected by apparatus responsive to the resenting a fa1lingrather than asingtem- 5 rate as well as to the degree of such changes. perature. Sucha control system is exemplified in U. S. Let- It is an object of thisinvention to eliminiate ters Patent #2,005,773, granted to Luis deFlorez, the above-described undesirable characteristic of June 25, 1935,in which patent disclosure is made control devices of this class by thesuperposition of two bellows elements jointly exerting theirreautomatically of a further control element, at 10 spective influencesthrough a floating lever on a once simple, effective, and positive inoperation, valve adapted to control the flow of a fluid meas well ascapable of universal application to a dium. One of the aforesaidelements comprises a wide variety of control devices in which theratesingle bellows unit acting directly on one end of of-change featureis incorporated. in the floating lever; and the other element com- Incarrying out the invention there is associaprises two opposed bellowsunits acting on the ted with such time-delayed .element a means otherend of the lever, the latter serving to comwhich is subject to acondition of the controlling municate to a valve a movementrepresentative fluid pressure for momentarily rendering the said of thejoint influence of the bellows elements. time-delayed elementinstantaneous in action. The opposed bellows members are adapted to beFor example, provision is made for by-passing the 20 actuated byinternal pressure of a control fluid constricted section between the twoopposed belfrom a common source-in this instance, the same lowselements.

source as the single unitand, by means of a con- The nature of theinvention, however, will best stricted section in the conduit leading toone of be understood when described in connection with the opposedbellows members, the action of the the accompanying drawing, in which:25 latter member is delayed relatively to the other, Fig. 1 is adiagrammatic representation of a thus introducing a time element in theultimate simple control system utilizing the principles of response ofthe opposed units. the invention.

This principle has been widely applied in var- Figs. 2 and 3 are sideand front elevations, re-

ious forms of automatic control devices and has spectively, to anenlarged scale and partly in sec- 30 effected material improvements inperformance, tion, of certain elements whereby the principles due to thetendency to anticipate the final deof the invention may be expeditiouslyexemplified. mand for correction in the controlled condition, Fig. 4 isa diagrammatic representation of a as based on the rate of change inthat condition. pneumatic control system utilizing the invention In theoperation of control devices of the genin a manner alternative to thatshown in Fig. 1. 35

eral nature hereinbefore set forth, there has been Referring to Fig. lof the drawing, I0 desigobserved one shortcoming, which becomes apnatesa closed vessel or enclosed space in which parent upon a reversal in thedirection of change it is desired to maintain by the admission of a. ofthe controlled condition. Considering such a suitable heating agent suchas steam, through a system applied to the regulation of temperaturevalve H, a constant temperature as determined 40 and the t mp r u to bem nif i en y by a sensitive bulb I2. The latter contains an to rise. theimmediate action of the expansible fluid and forms a part of a closedsystrol element would be to effect a reduction in flow tem including aregulator 3 which may be of of a heating agent, while the action of theauxrlany one of a Variety of types Well known the control element would,to temporanly art, but preferably of the form set forth in U. S. 45augment the action of the principal control, and, Letters Patent#1330247, granfied October 4, as conditlons approached a steady value,to with- 1932 draw this action. and leave the regulation entirelysubject to the primary control element.

with Such an arrangement, it will be apparent changes at the bulb l2,serves to control in an out that upon a Sudden reversal in the demandfor let conduit M the pressure of air derived from a control; i. e. asudden fall in temperature before constantpressure Source For purposesof the a t t f equilibrium was attained, t temporary disclosure, theregulating instrument may be takaction of the auxiliary control elementwould be n of the c nv n i n p n wh ch a r s in the the exact reverse ofthat required; and this undetemperature to which the sensitive bulb isex- 55 The regulator l3, in response to temperature posed tends toeffect regulation by a corresponding increase of air pressure in theconduit I4.

Operatively associated with the conduit I4 is a fluid-pressure-actuatedmotor element consisting of a single bellows member I6, adapted tochange its linear dimension with variations in internal fluid pressurederived from the conduit I4. Also connected to the conduit I 4 is asecondary control element II, consisting of a'pair of opposed bellowsmembers I8 and I9, acting on a common stem 20, to which is afiixed anarm 2| adapted to actuate external parts of the mechanism, as willhereinafter be set forth. Bellows member I8 is connected to the conduitI4 through a conduit 22. Bellows member I9 is connected to the conduitI4 through a. conduit 23 having therein a constricted or throttlingsection 24, whereby the flow of control fluid to and from the bellowsmember I9 is appreciably delayed.

The valve I I includes a stem member 26, and is internally arranged sothat the valve is opened as the stem is withdrawn from the body andclosed as it is forced thereinto. A floating lever 2'1, having threepivot points longitudinally disposed thereon, is pivoted at itsintermediate point to the stem 26 of the valve I I. To one end of thelever 21 is pivotally attached the bellows member I6 through means of alink 28, while to the remote extremity of the lever This attached thearm 2I through a link 29.

The apparatus as thus far set forth constitutes a well known form ofautomatic regulating device; and for it no invention is herein claimed.The auxiliary means through which improved performance is obtained, andfor which invention is herein claimed, comprises the following elements:A fluid-pressure-actuated valve 3| of the "direct-acting class, in whichthe valve is caused to close in response to the application of fluidpressure in its diaphragm chamber, and opened in response to a relief ofsaid pressure, is connected between the conduits I4. and 23, so thatwhen open it will provide free communication between the same, bypassingthe constricted portion 24 and rendering its time-delay characteristicineffective.

Compressed air (at a pressure of, say, 15 lbs.

per square inch) is supplied to the diaphragm chamber of the valve 3|from the constant pressure source through a conduit 32 having aconstricted portion 33. Communicating with the conduit 32 is a vent inthe form of an orifice member 34 having double-opposed jets 35. A vanemember 36 is adapted to swing about an axis 31 through a limited angle,as determined by stops 38 and 39, and to pass freely between the opposedjets of the orifice member 34.

Referring to Figs. 2'and 3, wherein is shown'a detail of the venting ororifice member; it will be seen that the vane member 36 has a slot orgap 48 in the intermediate part of its contour, so that, as the vaneswings about its axis 31, the jets 35 will be relatively unobstructedwhen the slot 46 is juxtaposed thereto with the vane in itsmid-position, and will be relatively obstructed by the vane member whenthe latter is at or near either limit of its swing, as determined by thestops 38 and 39.

Carried by a hub or spindle 31' coaxial with theaxis 31 and frictionallyengaged with the vane member 36, as, by a spring washer 4I and aclamping nut 42, is a lever arm 43 adapted-to swin'g about the axis 31and to carry with it the vane member 36,.except when the deflection ofthe vane member is limited by either of the stops 38, 39, when continueddeflection of the lever arm' 43 is permitted by the spring washer 4|.Thus, while the arm 43 may swing through a wide angle a as shown in thedrawing, the excursion of the vane 36 is limited to the relatively smallangle p.

A bellows member 44, operatively attached to the lever arm 43, as by alink 45, is placed in communication with the conduit I4, so that theangular position of the lever arm 43 about the axis 31 is dependent uponthe air pressure in the conduit I4. It will be apparent that, upon anychange in pressure in the conduit I4, the bellows 44 will deflect in acorresponding sense, and will similarly move the lever arm 43, which, inturn, will carry with it the vane member 36, until the latter engagesone or other of the stops, when the lever arm may continue to deflectwithout imparting further movement of the vane. It will further beapparent that, upon a reversal of direction of change of pressure in theconduit I4, the vane 36 will at once leave the stop against a which ithas been resting and will deflect toward the other stop, and that duringthe transition the slot 40 will pass between the jets 35, causing amomentary loss of pressure in the conduit 32, and a correspondingmomentary opening of the valve '3 I serving to by-pass the constriction24 and permit equalization of pressure in the bellows members I8 and I9,allowing them to assume their neutral or intermediate position ofbalance.

Following is a description of a typical operation of the control system.Assume there first to exist a steady-state condition, in which thesupply of heating agent through the valve II is exactly equal to thedemand, and the last previous action in the control system to have beenone on which air pressure in the conduit I4 was increased. This lastaction having been reflected in a linear extension of the bellows member44, the

vane 36 will have been-deflected toward the left, as shown in Fig. 1,and will be resting against the stop 38. The orifice member will thus beobstructed by the solid part of the vane, so that the valve 3I will beclosed and the constriction 24 will provide the only communicationbetween the bellows member I9 and the conduit I4.

Assume now that there takes place arise of temperature at the bulb I2.This, through the regulator I3, will effect an increase in pressure inthe conduit I4, with a corresponding. immediate action on the bellowsmember I6, and a tendency to close the valve II. At the same time thebellows member I8 will be extended in opposition to the bellows I9(whose response to change of air pressure in the conduit I4 will bedelayed due to the constriction 24) and will act through the floatinglever 21 to add its effect to that of the bellows I6. This will operateto further close the valve II, the auxiliary eflfect, however, beingsubsequently and gradually withdrawn as the pressure in bellows memberI9 becomes equalized with that in bellows I8 due to seepage of airthrough the constriction 24.

As thus far described, the performance set forth represents the normaloperation'of thedevice in its w ell-known form; and, under thecircumstancesv outlined, the temporary enhanced action of the controlvalve and subsequent withdrawal-of that action, due to the combinationof bellows members I8 and Hand the constriction 24, provides a desirableoperating characteristic. Assume, however, that shortly after there hastaken place a change in conditiomas outlined,

and before there has elapsed suflicient time to 75 enable the pressuresin bellows members I8 and to become equalized, the trend of regulationshould reverse. That is to say, a further change in demand for theheating agent occurs,

the same taking place in the reverse sense to the first-named change, sothat there will be a de-, mand for an opening, rather than a closing,ac-

' tion on the part of the valve Due to the normal action of thesubstantially instantaneous parts of the control system, as above setforth, the pressure in the conduit l4 will be lowered, with a consequentshortening of the bellows member I 6, which, acting on the left-hand endof the floating lever 21, will immediately tend 'to open the valve Thesecondary control system ll, however, being deflected in a sense toclose the valve II, and not yet having had suflicient time to return toa state of equilibrium, would normally be super-imposing on said valvethrough the lever 21 an action which for the time is the exact reverseof. that required to effect ideal control. Such action will continueuntil suflicient time has elapsed to permit establishment in bellowsmembers l8 and IQ of pressures having relative values similar to whatwould have been attained had the said bellows members been in a state ofequilibruim at the moment the last-mentioned change occurred.

Considering now the action of the auxiliary control mechanism, it willbe seen that upon the lowering of pressure in the conduit I4, consequentupon a demand for opening of the valve II, the bellows member 44, likethe bellows l6, will tend to collapse, decreasing its length. Thisaction operating through the lever arm 43 and the friction membersassociated therewith will at once deflect the slotted vane 36 away fromthe stop 38 toward the right-hand position, asshown in Fig. 3 of thedrawing, during the process of which deflection the orifice member 34will be momentarily opened as the slot 48 passes between the jets 35,causing a momentary loss of pressure in the conduit 32. This results ina corresponding momentary opening of the valve 3|, as hereinbefore setforth, whereby the constriction 24 will be by-passed and the pressuresin bellows members I8 and I9 allowed to equalize without delay, withresultant elimination of the above-mentioned undesirable performanceheretofore characterizing reversal of trend in the controllingrequirements.

In Fig. 4 is shown an alternative embodiment of the invention, which,while incorporating a principle identical with that hereinbefore setforth, presents a modified application of the same more in keeping withthe recognized practices of pneumatic control. In the drawing, 58designates a closed chamber in which it is desired to maintain by theadmission of steam or other suitable heating agent through apneumatically operated valve of the direct-acting class, a predeterminedand constant temperature, as determined by a sensitive bulb 52 placedwithin the chamber 58 and exposed to the atmosphere therein.

The bulb 52 contains an expansive or volatile fluid whose pressure willvary with the temperature to which the bulb is exposed, and is connectedby means of a capillary tube 53 to a Bourdon spring 54 forming a part ofa pneumatic regulator, which may be of the class 'set 'forth in theabove-cited Patent #1,880,247 and modified in the following manner: Athree-way valve 55 of the supply-and-waste type, adapted to receive airfrom a constant-pressure source 56 and to regulate the outgoing pressureof the same, is arranged to be operatively actuated by a bellows member51 in such a sense that increase of fluid pressure within said bellowsmember will cause the valve to lower the pressure of air delivered bythe valve 55, and vice versa. Bellows member 51 is placed incommunication withthe constant-pressure source 56 by a conduit 58having'a constricted portion 58; and connected to the conduit 58 is anorifice member 60 having double-opposed jets substantially as set forthin the above-mentioned Letters Patent #l,880,24'7. A vane member 6|. isadapted to swing through a limited angle about an axis or spindle 62,and to pass between the jets of the orifice member 68 in a sense more orless to obstruct the escape of air therefrom, and thereby govern theback-pressure in the conduit 58 and in the bellows member 51. Fixed tothe axis or spindle 62 is-a lever-arm 63, having pivotally attached toits extremity the mid-point of a floating lever 64. The lower end ofthis floating lever, as seen in the diagram, is attached by a link 65 tothe Bourdon spring 54.

Communicating with the outlet side of the valve member 55 is a conduit66, providing a direct connection to the diaphragm top of thepneumatically actuated valve 5|. This valve, being of the direct-actingclass, will tend to close with increase of pressure in the conduit 66,and vice versa.

Communicating also with conduit 66 is a pneumatic motor element 61comprising opposed bellows members 68 and 69, the former being in di-,rect communication with the conduit 66, and the latter through a conduit10, having a constricted portion Bellows members 68 and 69 are adaptedto act in opposition on a common stem 1|,and this stem carries an arm 12which is connected by means of a link 13 to the upper end, (as shown inthe drawing) of the floating lever 64.

Between conduits 66 and 18 is connected a direct-actingpneumatically-operated valve 14, having its diaphragm-top or motorelement in communication with the constant-pressure air source 56through a conduit having a constricted portion 16. Communicating withconduit I5 is an oriflce member 11 having a slotted vane 18 and adaptedto be actuated through a friction joint 19 from .a bellows member 88communicating directly with conduit 66, the construction and operatingprinciple of this element of the mechanism being identical with thatshown in Figs. 2 and 3.

The action of this embodiment of the invention may be analyzed asfollows: Consider a condition in which the temperature under controlmanifests a tendency to fall. This will be reflected in a decrease influid pressure within the bulb 52 and the Bourdon spring 54, and aconsequent deflection toward the left of the lower end of the floatinglever 64 and of the upper end of lever arm 63, whereby the vane 6| willbe deflected toward the orifice member 60, obstructing the same, andcausing the pressureof air in the conduit 58 to be increased, with acorresponding extension of the bellows member 51 and a movement of thevalve 55 in a sense to reduce air pressure in the conduit 66 and allmembers communicating therewith,

The immediate result of the reduced pressure in conduit 66 is to causethe valve 5| to open and increase the flow of heating agent to the spacewithin the chamber 58, thus tending to compensate for the tendencytoward falling temperature.

A secondary result of the reduction of pressure in the conduit 66 isfound in an'immediatecontraction of the bellows 68 and a retardedcontraction of the bellows 69. The response of bellows 68 will move theupper end of the floating lever 64 toward the left, tending to move thevane 6| further toward the orifice member 60, thus accentuating theoriginal action as above set forth. The subsequent response of bellows69, as the air pressure therein falls to that in the conduit 66 byseepage through the constriction 16, will restore the arm 12, the link13, and the upper end of lever 64 to their original positions, andremove the temporary effect of the pneumatic motor element 61. Thisprinciple in automatic control is well known in practice and for it noinvention is herein claimed.

The action of the auxiliary element 61 will thus be seen to beequivalent to that of the auxiliary device I! shown in Fig. l, and topossess the same well-known advantages in the control of varyingmagnitudes. A study of its operating characteristics will reveal here,however, as in other control devices of this type, that upon a reversalof the trend of control, as hereinabove set forth,

the time characteristic of the opposed bellowscombination maytemporarily defeat its purpose; and it is with .a view to eliminatingthis fault that there has been provided the by-passing valve 14 and theauxiliary devices adapted to effect its operation, which issubstantially equivalent to the action of valve 3|, whose performancehas hereinbefore been fully described.

Assuming again the condition of the trend of control being such as toeffect a lowering of pressure in the conduit 66, it will be seen thatwith the consequent tendency of the bellows 80 to collapse, the vane 18will be resting in the position shown and obstructing the. escape of airfrom the orifice member Ti. This maintains the air pressure on thediaphragm oi valve 14 and holds said valve in a closed position. Upon areversal of the trend of control, asreflected in a tendency of thepressure in conduit 66 to increase, the first increment of pressure inthis direction will tend to expand the bellows 80, causing the vane 18to be swung in a counter-clockwise sense to the lower stop, and, 'as theslotted portion thereof passes the orifice member TI, to release the airpressure in conduit 15 and in the diaphragm chamber of valve I4. Thesaid valve is thereby permitted to open momentarily, whereupon' thepressures in bellows 68 and 69 will be equalized and the combinationplaced in a condition to efiect its normal compensation performancewithout inhibitions persisting from the previous trend of control.

I claim:

1. In a fluid-pressure-actuated control system including a first bellowsmember and a second bellows member, together with a conduit connectingthe same and including a constriction whereby to delay the action of thesecond bellows member, and a source of fluid under pressureconnectedwith the first bellows member: a second conduit by-passing theconstriction of said firstnamed conduit, and a pressure-actuated valvecontrolling the passage of fluid through the former conduit, and meanssubject to the pressure applied to said first bellows to control saidvalve and including means to vary momentarily the pressure on'saidvalve.

2. In a fluid-pressure-actuated control system including a first bellowsmember and a second bellows member, together with a conduit connectingthe same and including a constriction whereby to delay the action of thesecond bellows member, and a source of fluid under pressure connectedwith the first bellows member: a second conduit by-passing theconstriction of said first-named conduit and a pressure-actuated valvecontrolling the passage of fluid through the former conduit, and meanssubject to the pressure applied to said first bellows to control saidvalve and including an orifice member in communication with theactuating means for the valve and an element cooperating therewithhaving a port to register with the orifice of said orifice member andmovable through the actuation of the means subject to the pressureappfied to said first bellows.

3. In an apparatus for controlling changes of temperature or pressure ina controlled system by means responsive to pressure changes in apressure system, a mechanical device communicating with said pressuresystem, which device first responds fully and immediately to a pressurechange in said system and then retracts said response in accordance withthe rate of said pressure change, means communicating with saidmechanical device for operating control devices 7 in said controlledsystem in accordance with changes efiected in said pressure system andtransmitted to said control devices through the conveying a fluid undercontrolled pressure to said first bellowsmember, a second conduit forconveying said fluid to said second bellows member, and including aconstriction whereby the response of said second bellows member to saidfluid pressure changes is delayed relatively to the response of saidfirst bellows: valve means, and fluid-pressure-actuated means operableupon a reversal of direction of a change in said system to open saidvalve means momentarily, and thereby by-pass said constriction andrender it for the time ineffective to introduce an element of delay.

5. In a fiuid-pressure-actuated regulating system havinga first bellowsmember and a second bellows member both adapted to respond to pressurechanges of a fluid, a first conduit for conveying a fluidunder'controlled pressure to said first bellows member, a second conduitfor conveying said fluid to said second bellows member, and including aconstriction whereby the response of said second bellows member to said'fluid pressure changes is delayed relatively to the response of saidfirst bellows: a fluid-pressure-actuated valve by-passing saidconstriction, a conduit for applying fluid under pressure to said valveto maintain the same in a closed condition, an orifice member in saidlast-named conduit, a constriction in said last-named conduit in advanceof the orifice member, a movable vane member adapted to obstruct theescape of fluid under pressure from said orifice, thereby main-"la-170,4 v

taining pressure on said valve and having an intermediate interruptedportion adapted when in juxtaposition to-the orifice oi. said orificemember to permit escape of fluid therefrom, the throttling effect ofsaid last-named constriction causing a corresponding releaseot pressureon said valve and opening of the same, a fluid-pressure motor element incommunication with said first bellows member, mechanical meansoperatively associating said motor element with said vane member, stopslimiting the excursion of said vane member in either direction to aportion of that corresponding to the normal range of deflection of saidmotor member, and a triction joint included in said mechanical means andadapted to yield in a sense to permit continued deflection of said motorelement'as said vane engages either of said stops.

6. In a fluid-pressure-actuated regulating sys-- sure-actuated valveIII-passing said constriction,

a conduit for applying" fluid under pressure to said valve to maintainthe same in a closed condition, an orifice member in said last-namedconduit, a constriction in said last-named conduit in advance of theorifice member, a vane mem-- ber movable in proximity to theorifice ofsaid orifice member and having solid end portions.

adapted to obstruct the escape of pressure fluid from the orifice,thereby causing pressure to be maintained on said valve and having anopen intermediate portion adapted to permit the escapefoi said fluidsubject to its flow through said last-named constriction, therebycausing pressure upon said valve to be released and the valvecorrespondingly opened, together with a fluid-pressure motor eleme t invcommunicatiojg with said first bellows member, mechanical meansoperatively associating said motor element with said vane member, stopslimiting the excursion oi said vane member in either direction to aportlon or that corresponding to the normal range of deflection of. saidmotor member, said vane, when limited by either stop resting in a,position in which one or its solid portions will be juxtaposed to saidorifice, and a friction joint included insaid mechanical means andadapted to yield and permit continued deflection of said motor element

